Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Response of a variable frequency switching constant on-time or adaptive
on-time controlled power converter to a large step-up or step-down change
in load is improved with a simple circuit that detects magnitude and
polarity of a change in output voltage and initiates, extends or
terminates conduction of power pulses from an input source through said
power converter. Both the amplitude and duration of undershoot or
overshoot of the transient response are reduced or, alternatively, the
capacitance of an output filter may be significantly reduced and still
provide comparable transient performance. The fast adaptive on-time
control is applicable to multi-phase power converters using phase
managers or one or more phase-locked loops for interleaving of power
pulses.

Claims:

1. A power converter including a power stage including a switching
arrangement and an inductor, a circuit for controlling on-time of said
switching arrangement, a detector for detecting a load transient, and a
control generator responsive to said detector for interrupting operation
of said circuit for controlling on-time of said switching arrangement.

2. The power converter as recited in claim 1, wherein said power stage
has a buck converter topology.

3. The power converter as recited in claim 1, wherein said circuit for
controlling on-time of said switching circuit provides constant on-time
control.

4. The power converter a recited in claim 1, wherein said control
generator extends duration of said on-time of said switching arrangement
upon detection of a load transient.

5. The power converter a recited in claim 1, wherein said control
generator terminates on-time of said switching arrangement upon detection
of a load transient.

6. The power converter as recited in claim 1, wherein said circuit for
controlling on-time of said switching circuit provides adaptive on-time
control.

7. The power converter as recited in claim 1, wherein said detector
discriminates between step-up and step-down load transients.

8. The power converter a recited in claim 7, wherein said detector
includes a band-pass filter, an emitter follower circuit, and a
comparator circuit applying a threshold to a detected step-up or
step-down load transient.

9. The power converter a recited in claim 1, wherein said detector
includes a band pass filter, an emitter follower circuit, and a
comparator circuit applying a threshold to a detected load transient.

10. The power converter a recited in claim 1, wherein said detector
includes a band-pass filter and a first comparator receiving an output of
said high frequency band-pass filter for comparison with a voltage less
than a reference voltage, and a second comparator receiving an output of
said high frequency band-pass filter for comparison with a voltage
greater than a reference voltage.

11. The power converter as recited in claim 10, wherein said first
comparator and said second comparator are transconductance amplifiers

12. The power converter as recited in claim 1 wherein an output of said
control circuit is applied directly to said circuit for controlling
on-time of said switching arrangement.

13. The power converter as recited in claim 1 wherein an output of said
control circuit is applied to a gate receiving an output of said circuit
for controlling on-time of said switching arrangement.

14. The power converter as recited in claim 1 wherein an output of said
control circuit is combined with an input voltage to said power converter
and the result applied directly to said circuit for controlling on-time
of said switching arrangement.

15. The power converter as recited in claim 1 wherein said power
converter is a multi-phase power converter.

16. The power converter as recited in claim 1 wherein interleaving power
pulses is performed using a phase manager.

17. The power converter as recited in claim 1 wherein interleaving of
power pulses is performed using a phase-locked loop.

18. A method of improving transient response of a power converter using
constant on-time or adaptive on-time control to provide power pulses to
an output of said power converter, said method comprising steps of
monitoring an output voltage of said power converter, band-pass filtering
said output voltage, determining polarity of a result of said high
frequency bandpass filtering step, and if said polarity of said result is
of a first polarity, initiating or extending a power pulse to said
output, or if said polarity of said result is of a second polarity,
terminating a power pulse to said output.

19. The method as recited in claim 18, including a further step of
applying a threshold to said result of said band-pass filtering step.

20. The method as recited in claim 19, wherein said threshold is
adjustable.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority of U.S. Provisional
Patent Application 61/973,600, filed Apr. 1, 2014, which is hereby
incorporated by reference in its entirety.

DESCRIPTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to variable frequency
switching power converters and voltage regulators and, more particularly,
to constant on-time power converters and voltage regulators and the
improvement of transient response to changes in power delivered to a
load.

[0004] 2. Background of the Invention

[0005] Virtually all electronic apparatus including semiconductor devices
require direct current power at a substantially constant voltage which
may be regulated within a specified tolerance even when the current drawn
by a load may vary over a wide range. For example, digital processor
semiconductor integrated circuits operating at high clock rates may
require very substantial amounts of power at very closely regulated
voltage for short periods of time between possibly extended periods in a
substantially stand-by state during which very little power is drawn.
Such power is generally provided from another direct current power source
at a voltage which may be subject to significant variation and must be
converted to the voltage and current required by a load circuit with as
high efficiency as possible. Consequently, variable frequency switching
power converters have been widely used because of their characteristic
high efficiency at light loads since switching frequency and consequent
switching losses are reduced when power delivered to a load is reduced.

[0006] Among the various arrangements known for operation as variable
frequency power converters are constant on-time (COT) power converters in
which power is supplied from an input power source for short and constant
periods of time as needed (between periods of at least a minimum duration
when power from an input source is interrupted and so-called freewheel
current is supplied from an inductor) to maintain a specified output
voltage from an output filter such as a filter capacitor as can be easily
determined by a very simple comparator circuit and a source of a
reference voltage. Such a filter capacitor also serves to supply power to
a load when the current drawn by the load increases sharply. Conversely,
the filter capacitor serves to reduce output voltage increase when the
current drawn by the load is sharply reduced. However, filtering voltage
changes during such transient changes in load may require very large
charge storage capacity of the output filter; limiting power density and
increasing cost of the power converter. Moreover, transient response of
constant on-time (COT) power converters may be largely unpredictable
depending on the relative timing of a load transient and the constant
duration periods during which power is drawn from the input power source.

[0007] For example, when a large increase in load power occurs, the power
converter response is limited by the constant on-time power pulses and
the limitation of switching duty cycle imposed by the maximum switching
frequency available and the minimum off-time alluded to above; generally
resulting in undershoot of the voltage response to a large transient
increase in required power. The degree of undershoot will be increased if
the increased load transient occurs at or very shortly after the end of a
constant on-time power pulse since the power converter cannot respond at
all until the minimum off-time has elapsed. Conversely, if load power in
transiently reduced at or shortly after the onset on a constant on-time
power pulse, the power converter current (e.g. inductor current)
supplying power to the filter will continue to increase until the end of
the power pulse; causing voltage overshoot.

[0008] In COT converters, the duration of the power pulse can generally be
freely chosen to meet power requirements of a given load. Accordingly,
so-called adaptive on-time (AOT) control has been widely used for
applications in which the load transients are relatively infrequent or
small. In AOT control, the duration of the power pulses is adaptively
adjusted in steady state operation to alter the switching duty cycle and
maintain a nearly constant switching frequency while operating in a
manner that is otherwise very similar to COT control. However, since the
duration of the power pulses may be very long or very short in steady
state operation and is only adjusted slowly, the degree of overshoot and
undershoot when a large load transient occurs is substantially increased.
Thus, while COT and AOT control is attractive for many applications, the
transient response has remained intractable.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to provide an
arrangement to increase or decrease on-time very quickly upon occurrence
of large step-up or step-down load transients during constant on-time
(COT) operation of a power converter with a single simple control circuit
that holds magnitude of undershoot and overshoot and the likelihood of
ringing to a very low level and does not affect the small signal
properties of COT control and can be simply implemented in an integrated
circuit.

[0010] In order to accomplish these and other objects of the invention, a
power converter is provided including a power stage including a switching
arrangement and an inductor, a circuit for controlling on-time of the
switching arrangement, a detector for detecting a load transient, and a
control generator responsive to the detector for interrupting operation
of the circuit for controlling on-time of the switching arrangement.

[0011] In accordance with another aspect of the invention, a method of
improving transient response of a power converter using constant on-time
or adaptive on-time control to provide power pulses to an output of the
power converter is provided comprising steps of monitoring an output
voltage of the power converter, (preferably high frequency) band-pass
filtering the output voltage, determining polarity of a result of the
filtering step, and if the polarity of the result is of a first polarity,
initiating or extending a power pulse to the output, or if the polarity
of the result is of a second polarity, terminating a power pulse to the
output.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The foregoing and other objects, aspects and advantages will be
better understood from the following detailed description of a preferred
embodiment of the invention with reference to the drawings, in which:

[0028] FIGS. 14 and 15 schematically illustrate further alternative
implementations of the invention, and

[0029] FIGS. 16 and 17 schematically illustrate application of the
invention to two types of multi-phase power converters.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0030] Referring now to the drawings, and more particularly to FIG. 1A,
there is shown a generalized schematic diagram of an exemplary constant
on-time (COT) control power converter 10 useful for understanding the
transient response problem addressed by the invention which is
illustrated in FIGS. 2 and 3. Operational waveforms of this power
converter are illustrated in FIG. 1B. Since this schematic diagram is
both generalized and arranged to facilitate an understanding of the
invention, no portion of any of FIGS. 1A-3 is admitted to be prior art in
regard to the invention. However, since the invention and its operation
are not illustrated therein, these Figures have been labeled "Related
Art". It should also be understood that while a so-called buck converter
is illustrated in these and other Figures for simplicity and general
familiarity to those skilled in the art, the invention is fully
applicable to any known or foreseeable power converter topology.

[0031] As is well understood in the art, a buck converter delivers power
from a power source 12 through an intermittently closed so-called top
switch 14 to inductor 16 which is connected to an output filter (depicted
as a capacitor Co and parasitic resistance RCo) and load
RL, depicted as a simple resistor although the load may include
reactive components and/or characteristics. So-called bottom switch 18 is
operated in a complementary fashion to top switch 14 so that when top
switch 14 is opened, a "freewheel" current is provided to inductor 16
from the current return path of the power converter through bottom switch
18. Thus, when top switch 14 is closed, the current through inductor 18
increases and a linearly increasing voltage is developed across inductor
18 that "bucks" the voltage applied from power input source 12. When top
switch 14 is opened and bottom switch 18 is closed, the voltage developed
across inductor 18 will continue to deliver power to the load while
voltage will linearly decrease. The increase and decrease in voltage
across inductor 18 appear as a ripple in the output voltage of the
converter and the ripple is reduced in magnitude to an arbitrarily low
level by the output filter. The filtered output voltage including the
ripple voltage is then compared with a reference voltage, VID, at
comparator 22 that, in the absence of providing constant on-time control,
can be used to directly control the operation of top and bottom switches
14 and 18. That is, when the load current and the ripple voltage causes
the output to diminish to the reference voltage, the output, Vc, of
comparator 22 will increase and control top switch 14 to supply power
from the input power source to inductor 18 to maintain the output voltage
at the desired (e.g. average) level.

[0032] As is well-understood in the art, using COT control the magnitude
of the ripple voltage may become very small at light loads and allow
power pulses to be initiated by small voltage fluctuations or noise,
causing a jittering of the power pulses and unstable operation that does
not accurately match load power requirements. To provide COT control in a
stable fashion, an additional ramp signal, ViL, is developed by
sensing the linearly increasing and decreasing inductor current with
sensor 20 (which is more reliable than sensing a low-level ripple voltage
that may contain noise) to which transfer function Ri is applied and
compared with control voltage VC at comparator 24 to initiate a COT
power pulse when ViL diminishes to equal VC at times S as shown
in FIG. 1B after a minimum off time has elapsed (e.g. after the
termination of the previous power pulse). A constant on-time can be
established in many ways that will be apparent to those skilled in the
art but, for simplicity and convenience of illustration, is illustrated
as being established by a set-reset flip-flop with a delay (e.g. an AND
gate with an RC circuit between the inputs) imposed between the set and
reset inputs) to provide a pulse train, D, to control the switches 14 and
18.

[0033] Use of the additional ramp and transfer function allows very high
control bandwidth design and the transient response can be made very fast
to allow the overshoot or undershoot to settle to steady state fairly
quickly. However, as will now be discussed in connection with FIGS. 2 and
3, the transient response can still be unacceptably slow and of
unpredictable magnitude, as alluded to above, particularly for providing
power to state-of-the-art semiconductor devices that may require power at
low voltages and stringent regulation tolerances.

[0034] Specifically and referring now to FIG. 2 (which may be regarded as
an extension to the right of FIG. 1B with additional Iload and
Vout waveforms), when a load step-up transient occurs, the output
voltage, Vout, is pulled down abruptly by the increased load current
drawn and the control voltage Vc rises sharply. The constant power
pulse width, Ton, is, however, fixed as is the minimum off-time,
Toff--.sub.min, and the duty cycle, D, becomes saturated while
IL is still incapable of being kept above Vc. That is, when
IL is below Vc, their intersection cannot cause initiation of a
further power pulse, but, rather, further power pulses are initiated
immediately after a minimum off-time, Toff--.sub.min, the time
required to charge the bootstrap capacitor of the high side gate driver
controlling the top switch and fixed by the system power stage and load,
has elapsed. Once IL*Ri has again exceeded Vc, The duty
cycle, D, may fall below saturation and steady state operation resumed.
It can clearly be seen that when Ton is relatively short and
Toff--.sub.min is relatively long, the undershoot of the
transient response can be quite large and subject to unpredictable
variation, depending on where the load step-up transient occurs in the
duty cycle, D, waveform.

[0035] Somewhat similarly, in the load step-down case, for a given power
stage or converter topology, overshoot can be very large if the load
transient occurs at or shortly after the beginning of a fixed duration
power pulse, Ton. In FIG. 3, the load step-down transient occurs
just after the beginning of the a power pulse. Vout initially rises
very sharply since the average current into the filter stage greatly
exceeds the current drawn and the portion of the COT power pulse after
the transient causes Vout to be pushed even higher, causing
overshoot, as shown by comparison with the dashed line that IL would
desirably follow if the power pulse was terminated by the step-down load
transient. It can be easily understood that the degree of overshoot will
be larger for longer Ton and duration subsequent to the step-down
load transient.

[0036] COT control implies variable frequency since off-time decreases to
increase duty cycle as load increases and vice-versa. While low switching
frequency increases efficiency for light loads, it can be a drawback in
many applications since the required frequency variation range can be
very large. Large frequency variation also make electromagnetic
interference (EMI) filter design very difficult. To alleviate problems
that may arise from COT control requiring widely varying frequency, so
called adaptive on-time (AOT) control has been employed and is widely
used in the voltage regulator (VR) industry. FIG. 3 schematically
illustrates a generalized architecture for and AOT control power
converter, again using a buck converter topology for simplicity and
familiarity to those skilled in the art. As with FIGS. 1A-3, FIG. 4 is
generalized and arranged to facilitate an understanding of the problems
addressed by the invention and, for that reason, no portion of FIG. 4 is
admitted to be prior art in regard to the present invention and FIG. 4
has thus also been labeled "Related Art".

[0037] Essentially AOT control is very similar to COT control except that
Ton may be adaptively changed to allow frequency range to be reduced
and, preferably, to assume a nearly constant frequency with duty cycle,
D, altered in accordance with the input voltage and the VID or Vref
command to accommodate small or gradual changes in load over the entire
load range.

[0038] The AOT control circuit is enclosed within dashed line 40 while the
remainder of the power converter is identical to that shown for the COT
control power converter as shown in FIG. 1A and discussed above although
many variations will be apparent to those skilled in the art. The signal,
S, that initiates power pulses is generated as discussed above but is
also used to control discharging of capacitor 46. As illustrated, the
input voltage Vin is input as VinT to control a variable
current source 42 providing charging current to capacitor 46 to provide a
voltage ramp signal as a positive input to amplifier 48. The voltage
control command VID or Vref is also applied as a negative input,
VrefT, to amplifier 48; the output of which terminates each power
pulse with an input to the reset input of a flip-flop. Thus, the current
source 42, capacitor 46 and amplifier 48 function in the manner of the
delay circuit determining Ton in FIG. 1 as discussed above with the
difference that Ton is now variable. Thus, it can be appreciated
that when operating at steady state where Ton is substantially
constant or only slowly varying, operation is substantially the same as
in COT control. However, it can also be appreciated that Ton can
become very short and comparable to Toff--.sub.min at small
duty cycle and cause an even larger undershoot for a step-up load
transient than caused by COT control. Conversely, Ton can also
become very long at high duty cycle and cause even larger overshoot than
under COT control when large step-down load transients occur. The
magnitude of overshoot and undershoot remains unpredictable, depending of
the time of occurrence of the load transient relative to the leading or
trailing edge of a power pulse for the same reasons discussed above in
connection with FIGS. 2 and 3.

[0039] Referring now to FIG. 5 the methodology and apparatus for producing
fast adaptive on-time (FastAOT or FAOT) control in accordance with the
invention will now be explained. The basic concept of FAOT is to increase
or decrease Ton immediately upon occurrence of a load transient. It
will be noted that the upper portion of FIG. 5 is identical to the AOT
control implementation shown in FIG. 4 including the AOT signal generator
40, described above with the addition of an AND gate 51 to provide pulse
train D to the switch driver circuit. The basic difference is that a FAOT
control generator 50 is provided and produces a VFAOT signal as a
reference voltage for amplifier/comparator 48 and a signal VOS to
the added AND gate 51.

[0040] The FAOT control generator 50 includes a preferably active, band
pass filter 52, preferably at a high frequency (preferably sufficiently
high to pass the highest anticipated slew rate of the load transient with
relatively low attenuation), referenced to VID (or Vref) that
detects the initial abrupt change in Vo (or Vout) and passes
only the high frequency part of the voltage change, VFLT, as shown
in curve b of FIG. 6, to the emitter follower stage 53, referenced to VID
or Vref, which truncates or blocks the low level, high frequency
ripple in VFLT as shown in curve c of FIG. 6. Thus only the large
peak in VFLT remains as VFAOT which is applied to
amplifier/comparator 48. It should also be noted that the fall-time of
the peak is significantly longer than the rise-time. A fast rise-time is
an important capability of the invention to provide fast transient
response while a longer duration fall time provides a smooth and seamless
return to steady-state operation which is a distinct advantage over use
of a differentiator circuit for transient detection. Since VFAOT is
used as a reference for amplifier/comparator 48, the ramp generator
supplying Vcap is allowed to charge to a higher value over an
extended period of time as shown in waveform d of FIG. 6 and immediately
increase Ton as can be seen in a comparison of operational waveforms
in Related Art FIG. 7 (without FAOT) and FIG. 8 (with FAOT). (To apply
the invention to a COT control power converter rather than an AOT control
power converter, VFAOT would simply be applied to disable or
interrupt the output of the delay Ton in FIG. 1; producing precisely
the same effect.) In FIG. 7, without the FAOT circuit, the duty cycle
becomes saturated during interval 70 while increase of actual load
current, Iload, is slowed by the minimum off-time periods and causes
Vo to be pulled down, causing a large undershoot. In FIG. 8, it is
seen that power pulses 80 and 82 have an extended Ton, allowing
Iload to increase much more rapidly and hold the undershoot to a
much lower level.

[0041] In the case of a step-down load transient, the FAOT circuit band
pass filter circuit detects a load transient as described above but since
this transient is a step-down transient, VFLT diminishes very
quickly, the emitter follower circuit 53 is turned off and no VFAOT
signal is delivered. Rather, VFLT is delivered to a comparator that
is referenced to a non-critical, user determined fraction (e.g. 80%) of
the VID (or Vref) signal (as can be provided from a simple voltage
divider). This comparison is, again, essentially a threshold for
truncation of VFLT and ripple elimination as shown in FIG. 9 such
that a value of VFLT above that fraction will have no effect on
overshoot or undershoot but values below that fraction of VID, indicating
a magnitude of step-down transient that will cause an undesirable degree
of overshoot) will keep the output of comparator 54 high and allow the
duty cycle waveform, D, to operate in a normal manner through AND gate
51. Provision of this comparison also allows the magnitude of step-up or
step-down transient that causes operation of FAOT circuit 50 to be
adjusted as desired. However, when VFLT falls below that level, the
output of comparator 54 drops to a low level and blocks waveform D as
shown in the respective waveforms of FIG. 9.

[0042] It should also be appreciated from the above discussion of FIG. 5
that the polarity of VFLT effectively selects circuit 53 or 54 to
extend or terminate a power pulse, respectively. By the same token,
either of circuits 53 or 54 could be omitted if it is desired to apply
FAOT exclusively to step-up or step-down load transients.

[0043] As will be evident to those skilled in the art, the components of
the FAOT circuits have very simple functions and can be embodied in many
ways other than those illustrated in FIG. 5. This blocking action can be
performed at any time and immediately upon occurrence of a step-down load
transient, including a time within a COT or AOT control pulse S to
immediately interrupt a power pulse as can be seen from a comparison of
power pulses 100 of FIGS. 10 and 110 of FIG. 11 to significantly reduce
the overshoot that would otherwise occur. It should also be noted from a
comparison of FIGS. 10 and 11 that the overshoot is reduced in both
magnitude and duration and is thus much less likely to cause the output
voltage to lose regulation or exceed regulation tolerance.

[0044] Referring now to FIGS. 12A and 123, while the magnitude of
undershoot and overshoot are largely unpredictable because of the random
timing of load transients, a quantitative evaluation of the improvement
in transient response can be obtained by considering the reduction in
output filter capacitance required to obtain substantially equivalent
transient response performance with and without FAOT in accordance with
the invention. FIG. 12A compares transient response using FAOT to AOT
control without FAOT using the same and larger filter capacitances in the
case of a step-up load transient. It can be seen that the same
capacitance value yields a significantly larger undershoot and that a
larger capacitor is required to obtain substantially equivalent
performance. Conversely, use of FAOT in accordance with the invention
allows an approximately 30% reduction in filter capacitance. Similarly,
FIG. 12B illustrates transient responses for step-down load transients
with and without FAOT for different capacitances. In this case, while
improvement in overshoot reduction with equal filter capacitance is 35 mV
which may seem small, the invention provides a 35% reduction in filter
capacitance to achieve comparable magnitude of overshoot while FAOT
further reduces the duration of overshoot significantly compared to AOT
and a larger filter capacitor.

[0045] In view of the foregoing, it is clearly seen that the invention
provides substantial reduction in undershoot and overshoot while still
maintaining the advantages of COT and/or AOT control using a single,
simple circuit that can easily be retrofit into any COT or AOT control
power converter where suitable connections to the power converter are
accessible. Additionally, since the change of Ton is proportional to
the output voltage change, the likelihood of ring back or other unstable
behavior is greatly reduced such as where the Ton change increment
and/or decrement is predefined. Moreover, the magnitude of the effective
Ton increment can be adjusted very simply by adjusting the gain of
band pass filter 52. Further, since alteration of Ton occurs only
during the transient period when the duty cycle would otherwise be
saturated, the invention does not affect the small signal properties of
COT control. Moreover, the FAOT circuit can be implemented in many ways
including the preferred implementation illustrated in FIG. 5, without
requiring any negative voltage to be present; allowing the FAOT circuit
to be informed or included within an integrated circuit.

[0046] The basic principles and operation having been described in detail
above, several additional and exemplary implementations will now be
discussed which will provide some additional performance advantages
and/or particular suitability for various applications. Other variant
implementations will become apparent to those skilled in the art.

[0047] Referring now to FIG. 13, a more generalized embodiment of
embodiment of the FAOT circuit of FIG. 5 will now be discussed. It will
be appreciated from a comparison of these two circuits that the emitter
follower circuit 53 of FIG. 5 has been replaced by comparator 131
connected similarly to comparator 54 except that VFLT is connected
to the positive input and the negative input receives a voltage in excess
of VID. Comparators 54 and 131 are preferably embodied as
transconductance amplifiers, as illustrated. The filter 52 remains
unchanged. In this embodiment, the ripple elimination, thresholding and
polarity detection of VFLT is performed by comparators 54, 131 and
adjustment of the thresholds for operation of the FAOT circuit can be
directly and independently set whereas, in the embodiment of FIG. 5
setting a step-up threshold would involve either design of emitter
follower 53 or alteration of gain of filter 52 and consequent adjustment
of the voltage applied to comparator 54.

[0048] Referring now to FIG. 14, an implementation providing additional
voltage control at VinT is shown. In this embodiment of the
invention, the FAOT signal is removed from the VrefT input of the
on-time generator to which Vref is then applied, and connected to a
negative input to an adder also receiving Vin and Vref on
positive inputs to be subtracted from the VinT input to the Ton
generator. Therefore, when undershoot at VO creates a peak at the
output of the emitter follower 53, the voltage at VinT will be lower
and proportional to the VO undershoot. This reduces the charging
current Iramp and the rate of increase of Vcap to increase
Ton.

[0049] It is also sometimes desired to use a phase-locked loop (PLL) to
cause the switching frequency to be constant or to synchronize switching
for multi-phase power converters. FIG. 15 illustrates an exemplary
implementation of the invention with a PLL. In this case, the FAOT signal
is generated in the same manner as in any of the
embodiments/implementation discussed above but is added to the low-pass
filtered output of a phase frequency detector that outputs a pulse train
of constant amplitude at a frequency corresponding to a phase or time
difference between input pulse trains (e.g. the Ton pulses and a
fixed frequency clock, fclk). Since the function of a PLL is to
adjust the duty cycle of the Ton pulses to develop the needed duty
cycle for a given load at the clock frequency rate, the combining of the
(positive or negative as in FIG. 13) FAOT signal with the Von signal
can increase or decrease Ton very quickly.

[0050] When it is desired to use a plurality of power converters in
parallel to supply power to a load, it is also desirable that power
pulses output from the respective, parallel connected power converters be
properly interleaved so that the power delivery will be evenly
distributed over time. Two types of interleaving arrangements commonly
used are using a phase manager to deliver signals to initiate Ton
pulses in sequence to the respective phases or to use PLLs synchronized
to fixed frequency clocks of different phases. Use of a phase manager is
the simpler of the two types of interleaving arrangements but has much
slower transient response.

[0051] Application of the invention to a multi-phase power converter using
a phase manager is shown in FIG. 16. In this embodiment, the output
voltage (which is regulated to match a reference voltage and develop a
control voltage Vc) is monitored as discussed above in connection
with FIG. 5 and the (positive or negative) output of the FAOT circuit
(see FIG. 13) circuit is input to each of the on-time generators; again,
as discussed above in connection with FIG. 5. This effectively provides
AOT control by Vin-Vref sensing with the inclusion of FAOT
using a single FAOT circuit to control all phases of the power converter.

[0052] Application of the invention to a multi-phase converter using PLLs
for inter-leaving is shown in FIG. 17. While a PLL is illustrated in the
power converter of each phase, a single PLL in one phase with a phase
delay for remaining phases or a combination thereof for larger numbers of
phases can also be used as disclosed in concurrently filed U.S. patent
application (Attorney's Docket Number VTIP14-066 (01640667AA)) which is
hereby fully incorporated by reference. Only a single FAOT circuit is
required to improve the transient response of all phases. The positive or
negative FAOT circuit output is added to the output of the PLL of all
phases as described above in connection with FIG. 15 and can quickly
extend or shorten any active Ton pulse being currently produced by
any phase or delay the start of the next Ton pulse of any phase of
the multi-phase power converter.

[0053] While the invention has been described in terms of a single
preferred embodiment, those skilled in the art will recognize that the
invention can be practiced with modification within the spirit and scope
of the appended claims.